An organic light emitting element is an electronic element having a positive (anode) electrode, a negative (cathode) electrode, and an organic compound layer disposed between both the electrodes. The organic light emitting element emits light when excitons generated by the recombination of holes and electrons injected from the respective electrodes in a light emitting layer contained in the organic compound layer return to the ground state. The recent organic light emitting device has remarkably advanced, and is characterized in that this organic light emitting device allows a thin and lightweight organic light emitting device which has low driving voltage, various emission wavelengths and rapid response to be produced.
Organic light emitting elements are broadly classified into fluorescent light emitting elements and phosphorescent light emitting elements according to the kind of excitons relevant to light emission. The phosphorescent light emitting element among them is an electronic element having a phosphorescent light emitting material in an organic compound layer constituting an organic light emitting element, specifically in a light emitting layer. The phosphorescent light emitting material absorbs energy generated by recombination of holes and electrons and generates triplet excitons. Thus, the phosphorescent light emitting element is an organic light emitting element capable of providing light emission originated from the triplet excitons.
Since the light emission quantum yield of phosphorescence can theoretically be made four times the quantum yield of fluorescence, attention has been focused on phosphorescent light emitting elements in recent years. However, there is room for further improvement in light emission efficiency in phosphorescent light emitting elements.
On the other hand, various proposals have been made on phosphorescent light emitting materials used in phosphorescent light emitting elements. As phosphorescent light emitting elements, for example, a compound H-1 (a thioxanthene compound, see Patent Literature 1) and a compound H-2 (a thioquinacridone compound, see Patent Literature 2) shown below are proposed.
